What is the minimum required groove depth of my drive ring?

Drive ring replacement
Over time the drive ring on your lapping jig will be worn away, this will be evident through the reduction of the groove depth when you invert the jig. When the grooves become shallow you can re-cut them if you have the necessary equipment (Logitech do not perform this service) and we would recommend that the new depth cut is 2.5mm. The second time this happens we recommend that you replace the drive ring, a replacement can be sourced fom Logitech